* lib/string.in.h (sigabbrev_np): New declaration.
* lib/sigabbrev_np.c: New file.
* m4/sigabbrev_np.m4: New file.
* m4/string_h.m4 (gl_HEADER_STRING_H_BODY): Test whether sigabbrev_np is
declared.
(gl_HEADER_STRING_H_DEFAULTS): Initialize GNULIB_SIGABBREV_NP,
HAVE_SIGABBREV_NP.
* modules/string (Makefile.am): Substitute GNULIB_SIGABBREV_NP,
HAVE_SIGABBREV_NP.
* modules/sigabbrev_np: New file.
* tests/test-string-c++.cc: Verify the signature of sigabbrev_np.
* doc/glibc-functions/sigabbrev_np.texi: Mention the new module.